We propose a new formulation for a photodissociation process to which an expansional (or algebraic) quantum‐variation‐method of scattering is applicable. By solving a ’’full collision’’ problem which describes a multichannel process on the repulsive surface, the photodissociation scheme takes account of interchannel coupling from the outset. Our expression for the amplitude of the partial linewidth is similar to that of the ’’half‐collision’’ approximation of Jortner e t a l. The present formalism differs in that the scattering wave functions take acount of interchannel coupling exactly. As a result, only on‐the‐energy‐shell contributions appear in the partial linewidth.